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[Xwayland] Add Xwayland byte-swapped clients support #738

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[Xwayland] Add Xwayland byte-swapped clients support #738

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7d195f5
[Wayland] Add Xwayland byte-swapped clients support
Sunderland93 Aug 12, 2025
0ded5cc
Use args for Xwayland and explicit disable byte swapped clients
Sunderland93 Aug 12, 2025
c168806
Typo
Sunderland93 Aug 12, 2025
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3 changes: 3 additions & 0 deletions config.h.meson
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@
/* Building with startup notification support */
#mesondefine HAVE_STARTUP_NOTIFICATION

/* Building with Sysprof profiling suport */

Check failure on line 52 in config.h.meson

View workflow job for this annotation

GitHub Actions / build / build (mint22, linuxmintd/mint22-amd64, Mint 22, true) / Mint 22 

suport ==> support
#mesondefine HAVE_PROFILER

/* Path to Xwayland executable */
Expand All @@ -70,3 +70,6 @@

/* Whether Xwayland has -initfd option */
#mesondefine HAVE_XWAYLAND_INITFD

/* Whether the Xwayland supports +/-byteswappedclients */
#mesondefine HAVE_XWAYLAND_BYTE_SWAPPED_CLIENTS
24 changes: 24 additions & 0 deletions data/org.cinnamon.muffin.wayland.gschema.xml.in
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Expand Up @@ -103,6 +103,30 @@
</description>
</key>

<key name="xwayland-allow-byte-swapped-clients" type="b">
<default>false</default>
<summary>Allow X11 clients with a different endianess to connect to Xwayland</summary>
<description>
Allow connections from clients with an endianess different to that
of Xwayland.

The X server byte-swapping code is a huge attack surface, much of
that code in Xwayland is prone to security issues.

The use-case of byte-swapped clients is very niche, and disabled by
default in Xwayland.

Enable this option to instruct Xwayland to accept connections from
X11 clients with a different endianess.

This option has no effect if Xwayland does not support the command
line option +byteswappedclients/-byteswappedclients to control that
setting.

Xwayland needs to be restarted for this setting to take effect.
</description>
</key>

</schema>

</schemalist>
38 changes: 25 additions & 13 deletions meson.build
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Expand Up @@ -376,6 +376,7 @@ if cc.has_header_symbol('sys/prctl.h', 'prctl')
endif

have_xwayland_initfd = false
have_xwayland_byte_swapped_clients = false
if have_wayland
xwayland_dep = dependency('xwayland', required: false)

Expand Down Expand Up @@ -416,6 +417,16 @@ if have_wayland
if (have_xwayland_initfd)
cdata.set('HAVE_XWAYLAND_INITFD', 1)
endif

# For Xwayland +/-byteswappedclients usage
if xwayland_dep.found()
have_xwayland_byte_swapped_clients = xwayland_dep.get_variable('have_byteswappedclients',
default_value: 'false') == 'true'
endif

if (have_xwayland_byte_swapped_clients)
cdata.set('HAVE_XWAYLAND_BYTE_SWAPPED_CLIENTS', 1)
endif
endif

#xwayland_grab_default_access_rules = get_option('xwayland_grab_default_access_rules')
Expand Down Expand Up @@ -465,19 +476,20 @@ output = [
'',
' Options:',
'',
' Wayland.................. ' + have_wayland.to_string(),
' Wayland EGLStream........ ' + have_wayland_eglstream.to_string(),
' Native Backend........... ' + have_native_backend.to_string(),
' EGL Device............... ' + have_egl_device.to_string(),
' Default driver........... ' + default_driver,
' Remote desktop........... ' + have_remote_desktop.to_string(),
' gudev.................... ' + have_libgudev.to_string(),
' Wacom.................... ' + have_libwacom.to_string(),
' SM....................... ' + have_sm.to_string(),
' Startup notification..... ' + have_startup_notification.to_string(),
' Introspection............ ' + have_introspection.to_string(),
' Profiler................. ' + have_profiler.to_string(),
' Xwayland initfd.......... ' + have_xwayland_initfd.to_string(),
' Wayland.......................... ' + have_wayland.to_string(),
' Wayland EGLStream................ ' + have_wayland_eglstream.to_string(),
' Native Backend................... ' + have_native_backend.to_string(),
' EGL Device....................... ' + have_egl_device.to_string(),
' Default driver................... ' + default_driver,
' Remote desktop................... ' + have_remote_desktop.to_string(),
' gudev............................ ' + have_libgudev.to_string(),
' Wacom............................ ' + have_libwacom.to_string(),
' SM............................... ' + have_sm.to_string(),
' Startup notification............. ' + have_startup_notification.to_string(),
' Introspection.................... ' + have_introspection.to_string(),
' Profiler......................... ' + have_profiler.to_string(),
' Xwayland initfd.................. ' + have_xwayland_initfd.to_string(),
' Xwayland byte-swapped clients.... ' + have_xwayland_byte_swapped_clients.to_string(),
'',
' Tests:',
'',
Expand Down
2 changes: 2 additions & 0 deletions src/backends/meta-settings-private.h
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Expand Up @@ -79,6 +79,8 @@ void meta_settings_get_xwayland_grab_patterns (MetaSettings *settings,

gboolean meta_settings_are_xwayland_grabs_allowed (MetaSettings *settings);

gboolean meta_settings_are_xwayland_byte_swapped_clients_allowed (MetaSettings *settings);

MetaX11ScaleMode meta_settings_get_x11_scale_mode (MetaSettings *settings);

void meta_settings_enable_x11_fractional_scaling (MetaSettings *settings,
Expand Down
22 changes: 22 additions & 0 deletions src/backends/meta-settings.c
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Expand Up @@ -72,6 +72,9 @@ struct _MetaSettings
GPtrArray *xwayland_grab_blacklist_patterns;

MetaX11ScaleMode x11_scale_mode;

/* Whether Xwayland should allow X11 clients from different endianess */
gboolean xwayland_allow_byte_swapped_clients;
};

G_DEFINE_TYPE (MetaSettings, meta_settings, G_TYPE_OBJECT)
Expand Down Expand Up @@ -498,6 +501,15 @@ update_xwayland_allow_grabs (MetaSettings *settings)
"xwayland-allow-grabs");
}

static void
update_xwayland_allow_byte_swapped_clients (MetaSettings *settings)
{

settings->xwayland_allow_byte_swapped_clients =
g_settings_get_flags (settings->wayland_settings,
"xwayland-allow-byte-swapped-clients");
}

static void
wayland_settings_changed (GSettings *wayland_settings,
gchar *key,
Expand All @@ -512,6 +524,10 @@ wayland_settings_changed (GSettings *wayland_settings,
{
update_xwayland_grab_access_rules (settings);
}
else if (g_str_equal (key, "xwayland-allow-byte-swapped-clients"))
{
update_xwayland_allow_byte_swapped_clients (settings);
}
}

static void
Expand Down Expand Up @@ -541,6 +557,12 @@ meta_settings_are_xwayland_grabs_allowed (MetaSettings *settings)
return (settings->xwayland_allow_grabs);
}

gboolean
meta_settings_are_xwayland_byte_swapped_clients_allowed (MetaSettings *settings)
{
return settings->xwayland_allow_byte_swapped_clients;
}

MetaX11ScaleMode
meta_settings_get_x11_scale_mode (MetaSettings *settings)
{
Expand Down
52 changes: 38 additions & 14 deletions src/wayland/meta-xwayland.c
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Expand Up @@ -580,6 +580,10 @@ meta_xwayland_start_xserver (MetaXWaylandManager *manager,
GSubprocessFlags flags;
GError *error = NULL;
g_autoptr (GTask) task = NULL;
MetaBackend *backend;
MetaSettings *settings;
const char *args[32];
int i;

task = g_task_new (NULL, cancellable, callback, user_data);
g_task_set_source_tag (task, meta_xwayland_start_xserver);
Expand Down Expand Up @@ -614,6 +618,9 @@ meta_xwayland_start_xserver (MetaXWaylandManager *manager,
flags |= G_SUBPROCESS_FLAGS_STDERR_SILENCE;
}

backend = meta_get_backend ();
settings = meta_backend_get_settings (backend);

launcher = g_subprocess_launcher_new (flags);

g_subprocess_launcher_take_fd (launcher, xwayland_client_fd[1], 3);
Expand All @@ -624,23 +631,40 @@ meta_xwayland_start_xserver (MetaXWaylandManager *manager,

g_subprocess_launcher_setenv (launcher, "WAYLAND_SOCKET", "3", TRUE);

manager->proc = g_subprocess_launcher_spawn (launcher, &error,
XWAYLAND_PATH,
manager->public_connection.name,
"-rootless",
"-noreset",
"-accessx",
"-core",
"-auth", manager->auth_file,
"-listen", "4",
"-listen", "5",
"-displayfd", "6",
i = 0;
args[i++] = XWAYLAND_PATH;
args[i++] = manager->public_connection.name;
args[i++] = "-rootless";
args[i++] = "-noreset";
args[i++] = "-accessx";
args[i++] = "-core";
args[i++] = "-auth";
args[i++] = manager->auth_file;
args[i++] = "-listen";
args[i++] = "4";
args[i++] = "-listen";
args[i++] = "5";
args[i++] = "-displayfd";
args[i++] = "6";
#ifdef HAVE_XWAYLAND_INITFD
"-initfd", "7",
args[i++] = "-initfd";
args[i++] = "7";
#else
"-listen", "7",
args[i++] = "-listen";
args[i++] = "7";
#endif

#ifdef HAVE_XWAYLAND_BYTE_SWAPPED_CLIENTS
if (meta_settings_are_xwayland_byte_swapped_clients_allowed (settings))
args[i++] = "+byteswappedclients";
else
args[i++] = "-byteswappedclients";
#endif
NULL);

/* Terminator */
args[i++] = NULL;

manager->proc = g_subprocess_launcher_spawnv (launcher, args, &error);

if (!manager->proc)
{
Expand Down
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